1. Field of the Invention
The present invention relates to a method of manufacturing an organic EL (Electroluminescent) display.
2. Description of the Related Art
In recent years, displays using organic EL elements have been developed. In an organic EL element, a light-emitting layer is sandwiched between a pair of electrodes. The organic EL element emits light at a luminance corresponding to a driving current which flows between the electrodes.
In the manufacturing process of an organic EL display, when a low-molecular organic substance is used as a material of a light-emitting layer, vacuum deposition is used to form the light-emitting layer. Alternatively, when a polymeric organic substance is used as a material of a light-emitting layer, a method is employed in which a film is formed by applying a solution containing a polymeric organic substance and dried.
In either case, an anode and a cathode may short-circuit due to partial absence in a light-emitting layer. As a result, the organic EL element is recognized as a dark spot. Even without any short circuit between an anode and a cathode, if the characteristic of an organic EL element deviates from those of other organic EL elements, the former organic EL element is recognized as a dark spot or a bright spot.
Such a luminance shift can also occur due to another factor when active matrix driving is executed by arranging a drive transistor for each pixel. For example, if the characteristic of the drive transistor for a pixel deviates from those of the drive transistors for other pixels, the former pixel is recognized as a dark spot or a bright spot.
Of the above-described luminance shifts, the dark spot is difficult to be recognized as compared to the bright spot. The bright spot can be made more unnoticeable by changing it to a dark spot. This can be done by, e.g., fusing the interconnection which connects the drain of the drive transistor included in the bright spot pixel to the anode of the organic EL element by irradiating the interconnection with the second harmonic of a YAG laser.
For the dark spot generated by the short circuit between the anode and the cathode, it is effective to employ a structure in which the each anode is constituted by a plurality of conductive layers spaced apart from each other and the conductive layers are connected to the drain of the drive transistor through interconnections, respectively. More specifically, according to this structure, when disconnecting only the interconnection, which connects the conductive layer short-circuited with the cathode to the drain of the drive transistor, by fusion using laser beam irradiation, the conductive layer short-circuited with the cathode can be insulated from the remaining conductive layers included in the same pixel. Hence, the pixel can be suppressed from being recognized as a dark spot.
The cathode is formed as a common electrode. For this reason, it cannot be confirmed by using transmitted illumination whether the interconnection has been disconnected by fusion using laser beam irradiation. To confirm it, reflected illumination is used. However, it is difficult to distinguish reflection by the interconnection surface made of a metal from that by the cathode surface.
To disconnect a metal by fusion, very large energy is necessary because of its high reflectance, or viscosity or fluidity in a melted state. Hence, when the interconnection is disconnected by fusion using laser beam irradiation, its peripheral portion is readily damaged. For example, the insulating layer between the interconnection and the cathode may break so that they may short-circuit. Alternatively, an interconnection which should not be disconnected may also be disconnected by fusion.